1. Field of the Invention
The present invention relates generally to a display control in a computer system and more particularly to a method of and an apparatus for controlling the display of video signal information on the display devices of different types which are usually connected as output devices to an external micro computer or other control systems for use in a process control application or other applications. The display devices to which the present invention applied are display units that employ a liquid crystal display (LCD) element and other similar display elements. Those display devices may provide output video signal information in visible character, tabulated, or graphical form.
2. Description of the Prior Art
In the process control field, for example, various types of display devices are used as visual output devices for presenting on their screens the video signal information which is delivered from their attached microcomputer or other process control system. It is also known that the display devices are used in other computer applications so as to provide an easy and direct means of a man-to-machine communication or interface. The display devices currently available in the computer system configuration range widely from the television-type displays employing a CRT screen such as monitor TV and home-use TV receivers to other display units of the type that employs a liquid crystal display (LCD) element and other similar display elements. In most cases, those display devices provides a display of the output data of the main computer system in a character form or graphical representation in colors or monochrome. When a computer system is configured to include display units, the display devices are usually connected to the central processor (CPU) through appropriate channels and display controls. In this case, the display controls only provide the sequence control and buffering facilities. All the display devices mentioned above that are available for commercial use, however, have hardware and software limitations on their display capabilities. In other words, the number of characters, the kind of colors, and the contents of graphical representation such as shapes, graphs, etc. that the display devices are capable of presenting at a time on their screens are all limited. The conventional display controls are not designed to provide such control functions as to permit the display devices to display all output information at a time as required. The performance or capabilities of the computer system are restricted by the hardware and software limitations on the display devices, and therefore cannot be utilized completely or effectively.
When the operation of the computer system involves the operation of the display devices; therefore, the optimum use of the computer performance or functions is practically impossible, leaving the most part of its performance not utilized. When the computer system provides output video signals, the display device that can display the video signal information is limited to the type of display device which employ a CRT screen, such as monitor television receiver and home-use television receiver. If it is desired that the video signal information be displayed on the other types of display devices that employ an LCD element or other similar display element, appropriate hardware and software implementation must be built in the microcomputer package in order to handle or process the video signals to allow those display devices to display the visual information based on the processed video signals. However, a great amount of development efforts and costs must be required for this implementation.